is a mineral that occurs naturally in almost all foods and water supplies. The ion comes from the element fluorine. Fluorine, the 13th most abundant element in the earth's crust, is never encountered in its free state in nature. It exists only in combination with other elements as a compound. is effective in preventing and reversing the early signs of tooth decay. Researchers have shown that there are several ways through which fluoride achieves its decay-preventive effects. It makes the tooth structure stronger, so teeth are more resistan ....